Due to recent improvement on an operation rate of a device, higher reliability on a high-voltage electric power device is earnestly demanded more than ever. Known typical factors of troubles which may jeopardize reliability of such high-voltage electric power devices are insulation deterioration and a breakdown phenomenon. As a detecting means for an insulation defect that may cause such insulation deterioration and breakdown, partial discharge measurement is widely used now. Further, there is also a proposed partial discharge measurement method whereby not only existence but also a position of a partial discharge defect is located. For example, there is a related art described below as such a detecting means for a partial discharge defect position. According to this related art, a partial discharge measurement sensor circumferentially swept along a surface of a stator winding of a rotating machine, and the partial discharge defect position is located by detecting a position where intensity of a measured signal becomes highest. Alternatively, a position of a partial discharge defect is located by detecting a position where a difference of arrival time between signals measured by a plurality of sensors becomes largest. This kind of method is effective in a low-voltage rotating machine where there is extremely few number of partial discharge defects and measurement can be easily performed in an environment with little ambient noise, such as a shield room, because a sample size is small. However, in a high-voltage device represented by a high-voltage generator and a motor that may have numerous partial discharge defects inside an insulation layer, partial discharge occurs at a plurality of positions. Therefore, a position where signal intensity is highest or a difference of signal arrival time is largest does not clearly appear, and the partial discharge defect position can be hardly detected. Further, in general, the high-voltage device has large capacity and a large size. Therefore, the high-voltage device can be hardly brought into a shield room for testing, and in many cases, partial discharge has to be measured in an environment with much ambient noise. Under such an environment, there may be problems in which noise intrudes inside measurement data while the sensor is swept around, and correct signal intensity distribution of partial discharge cannot be measured. Moreover, even though the partial discharge defect position can be located, there is a difference in a risk between a defect extending in an electric field direction and a defect extending in a direction orthogonal to the electric field. Therefore, a site having a large apparent charge of partial discharge is not always a defect position having a high risk, and there may be a problem in which risk assessment cannot be performed only with intensity distribution of partial discharge signals.
To solve such a problem in risk assessment, attempted in recent years is a method in which a risk of a defect is diagnosed by measuring a following pattern: a voltage phase of partial discharge occurrence-an apparent charge of partial discharge-number of occurrence of partial discharge (hereinafter, abbreviated as pattern φ-q-n). However, even in this method, the patterns φ-q-n of a plurality of partial discharge signals are superimposed in a high-voltage rotating electrical machine having numerous partial discharge defects, and there may be problems in which defect detection in a product and risk assessment cannot be correctly performed.